Here’s episode two (of four) of my conversation with WREK scientist/DJs Pete Ludovice and Bill Hung. In this bit we’re talking about whale shark research in Mexico and the idea of conservation by payment for ecosystem services. Check out the rest of their archive here, and listen live on Wednesdays at 12 (details in the link)
Entries in whale sharks (38)
I am excited to say that I will be joining the Deep Sea News network of marine science bloggers. For those who are not familiar with DSN, they’ve been producing kick-butt marine science bloggy-type content since 2005 and are currently the most popular marine bio blog on the web and the only one listed in Google News. Joining that community means I can work with some of the best mar-sci bloggers around and hopefully we all riff off each other to produce great content and host the sort of excellent discussions that I have always found so rewarding about blog audiences. Its a sort of critical mass that’s much more manageable in a blog network than going solo.
I am going to hang onto this domain, because there will be times when I want to write about stuff that is not DSN material, so don’t drop this page from your feed reader just yet.
My first post is a general intro to the natural history of whale sharks and may be very familiar to folks who’ve followed this blog for a while. Once its set up, I’ll post the link to RSS feed of my posts at DSN here. But really, you should subscribe to ALL of DSN’s stuff, you can’t go wrong.
After the outrageous popularity of a previous post here about a whale shark dookie so big you could see it from an aeroplane, now this YouTube video of a white shark telling some cage divers exactly what he thinks of their taste in SCUBA fashions:
At the risk of being labeled “Dr Shark Poo”, I have a few quotes in this article discussing exactly what’s going on here. In short, why is the poop yellow? (digestive and blood pigments) why are the fish eating it? (nom nom nom) and why study shark poo anyway? (a figurative treasure trove of physiological data). Roll over there and check out the rest of the article.
BMW has a promotional docu-video thing out that opens with former astronaut Buzz Aldrin talking about how he once took a ride on a whale shark and how that’s the kind of effortless transport mechanisms we need these days. Actually, what we need these days is for people to not promote the harassment of marine life, for former astronauts to stick to being former astronauts, and for BMW to not promote and disseminate this kind of misinformation. I don’t use the FAIL meme all that often, but this one earns it fair and square…If you want “mobility” Buzz, stick to a Hoveround
Tip of the ol’ astronaut’s helmet to Jim Tharpe
Or at least leucistic, based on what appears to be a bit of pigment at the base of the pectoral fin and, possibly, in the mouth (though those could be small remoras). This was shot by a tour boat guide in the Galapagos and appears to show a female whale shark with no spots because she’s pure white. I even hazard that she might be pregnant, given the slight bluge in the area above her pelvic fins. Very cool
Recently I featured a piece about how turtle hatchlings change their movement strategy several times in just the first few hours of life in order to suit their changing needs as they move across different types of sand. Well, to go from the sublime to the ridiculous (or rather, just from the really small to the truly gargantuan) there’s a new paper out that shows that whale sharks, too, adjust the way they move according to their needs. This new work follows nicely after Phil Motta’s paper earlier this year, also discussed here, which took a comprehensive look at how whale sharks feed. Between them they make big strides in the autecologyof whale sharks. The new paper, by Adrian Gleiss and Rory Wilson from Swansea University and Brad Norman from ECOCEAN, describes work they did at Ningaloo reef in Western Australia, perhaps the world’s best studied aggregation area for whale sharks. They took a new type of accelerometer tag developed in Rory’s lab called a “daily diary” and deployed them on wild whale sharks to measure not only where they are (like traditional wildlife satellite tags) but also details about what the animals were doing: the beating of their tails and the rientation of their bodies in 3 dimensions. From this information they could basically reconstruct the animal’s actions with computer game-like accuracy (indeed, the software looks a lot like something for the X-Box!). The findings show an animal with a surprising diversity of movement modes and a sophisticated approach to minimising the amount of energy they spend moving through the ocean. They also help explain one of the most enduring mysteries of whale shark biology - a curious pattern of super-deep dives over the abyssal depths.
The first big observation is that whale sharks have 4 different types of dives and that these probably serve different purposes. It was well known from traditional tagging studies (sat tags record depth data as well as location) that whale sharks dive quite a lot throughout the day, but the new daily diary tags showed that not all dives are the same and, in fact, they could be easily discriminated as one of four main types based on what the depth profile looks like: yo-yo (probably searching), V (horizontal movement), U (feeding at depth), and bottom bouncing (searching at depth).
The second and a really key finding is that all the dive types feature a gliding descent and an active ascent. In other words, they don’t beat their tails on the way down, but they do on the way up. Gliding converts their negative buoyancy (a sort of potential energy) into horizontal and vertical movement (kinetic energy). The fact that their dive has both vertical (depth) and horizontal (forward motion) components, without active use of the tail, shows that their bodies are adapted to convert sinking to swimming. Most of that effect comes from their pectoral fins, which serve as wings for gliding, but there is probably a big contribution from that incredibly broad head, which serves as a sort of lifting canard, a flat plane that creates lift at the front end. Gliding is an extremely efficient way to move; not only are they not spending energy operating their musculature to beat the tail through the water to create thrust, but the drag coefficient of water across their skin is a third as much when they glide as when they are actively beating their tails.
The third finding, which Gleiss and friends really go into in some, ahem, depth, is that angle of descent and ascent is consistently different for each type of dive and that they are optimal for whatever the purpose is. For example, a V dive is meant to cover a great horizontal distance, so the gliding descent is at a shallow angle and the ascent angle is the one that minimizes the amount of energy spent to gain horizontal distance. In contrast, the angles of a yo-yo dive minimize the amount of energy spent to gain vertical distance. The important point is that for any given purpose there is an optimal angle - one that uses the least energy for the most benefit - for both descent and ascent components. Whale sharks adapt the geometry of their dives to stay in that optimum zone and minimize the amount of energy they spend on whatever they are doing. Clever right? Well, its probably not a conscious decision, but rather a state of tremendous efficiency towards which they have evolved: natural selection is a powerful tutor.
In the course of their study, the researchers solved one of the great mysteries of whale shark biology: the extraordinary deep dives whale sharks do when they are over abyssal depths (see the Brunnschweiler reference). These dives tend to happen around dawn and dusk and may exceed 1600m or more in depth; in fact, we don’t know just how far down they go, because most tags have a self-preservation device that cuts them free of the animal at 1600m, lest the tag be crushed by the immense pressure of the overlying water. We’re talking depths enough to turn a Styrofoam coffee cup into a shrinky-dink thimble, as well as changing enzyme kinetics and making the urea in their blood greatly more toxic, so the motivation to dive so deep must be compelling. There had been suggestions that they go down to rid themselves of parasites (as a parasitologist, I never bought that: parasites would easily co-evolve to tolerate such a strategy), or to clean their filter plates (at those depths particulate organic matter redissolves!) or even to “sleep”, although there is no evidence that sharks do so. Well, it turns out that they are dives of the V type, optimised to spend the least amount of energy while achieveing maximum horizontal movement (HD in the figure above). In other words, to travel far, they glide deep, and then gently beat their tails and ascend at a very shallow angle (steeper angles costing more energy and achieving less horizontal distance). This is a strategy best used during migratory phases when travelling, not feeding, is your number one priority.
To recap then, whale sharks turn out to have at least 4 main types of dives, each serving a different purpose from feeding to horizontal travel, and the geometry of each type of dive is optimised to achieve the goal while minimising the energy cost. Overall, it paints a picture of an animal that is a paragon of efficiency, which is understandable given that they dwell in the nutrient-poor surface waters of the tropics, which are typically much less productive than the rich cold temperate and Arctic seas frequented by their fellow filter feeders: basking sharks and baleen whales. I suspect that future studies will show that whale sharks deploy these movement strategies to travel efficiently between hotspots of tropical productivity, be they fish spawning events or patches of seasonal tropical upwelling, and that they are therefore extremely strategic masters of the feeding/travelling trade-off.
Gleiss, A., Norman, B., & Wilson, R. (2010). Moved by that sinking feeling: variable diving geometry underlies movement strategies in whale sharks Functional EcologyDOI: 10.1111/j.1365-2435.2010.01801.x
Brunnschweiler, J., Baensch, H., Pierce, S., & Sims, D. (2009). Deep-diving behaviour of a whale shark during long-distance movement in the western Indian OceanJournal of Fish Biology, 74(3), 706-714 DOI: 10.1111/j.1095-8649.2008.02155.x
Check out this cool bit of footage from our recent research visits to Mexico to study whale sharks with the Georgia Aquarium team. We were diving under a large aggregation of whale sharks when one of them broke from the surface to come and visit, checking out first one diver, and then the other, possibly attracted by the bubbles. Whale sharks normally cruise around at the surface, largely indifferent to human presence except for occasionally rolling their eye across you as they pass, but this one was clearly interacting with us. Colleague Betty Galvan tells me about a small (if 4m could be considered small) female that followed her for 20 minutes in Honduras one time, so interactive she described it as being like a puppy. I suspect, when conditions are right, whale sharks can be curious or even inquisitive critters. Its hard to prove, but I don’t think there’s much doubt from the video. The aquarium has been conducting a behavioural study on the collection animals for some time, but more work on their behaviour in the natural setting is desperately needed. Hopefully the aquarium study can refine the techniques needed to get out there and understand what they do in the field.
Most people consider remoras to be no-good hangers-on, sponging off well-meaning marine megafauna. But on one of our research trips to Mexico to study whale sharks this summer, one of the staff divers, Elliott Jessup, had an incredible encounter with one of the most inquisitive fish any of us have ever seen, and scientist/videographer Bruce Carlson caught the whole thing in HD. The waters were full of whale sharks and their attendant remoras, when this little guy took leave of his usual hosts and instead took a real liking to Elliott, even attaching to his butt, and eating his hair. Learn more about our whale shark research here and you can follow my YouTube channel here and the Georgia Aquarium channel here.
The footage is copyright 2010 Bruce Carlson/Georgia Aquarium and used with permission.
My ECOCEAN colleague Brad Norman has been deploying Crittercam on some whale sharks in Exmouth, Western Australia. I always wanted to try that; I’m so glad he did it! The footage is now on National Geographic. There’s a bit less actual Crittercam footage in the story than I would have liked, but thats just my own anxiousness to see what they see! My guess is that a lot of it was much like the snippets shown - slowly cruising near the surface.
I would LOVE to see what they see approaching food patches, or when they see another whale shark, or on one of their mysterious crepuscular dives (might need some supplemental lighting for that one). Its a great start.
Manta Ray training - Dennis Christen and other training staff talk about what it takes to train the giant rays
Invasive Lionfish - biologist Heather Dziedzic discusses the spread of the beautiful but destructive lionfish throughout the Atlantic states and Caribbean
Giant Pacific Octopus - features a nice photo of the aquarium’s octopus
I’m really excited about a new paper that’s finally out about how whale sharks feed, from the way their filter pads are built to what they eat and how much. I’m not an author on the paper but I’ve been a witness to a lot of the work and its terrific to see it come to fruition. So who’s it by and what’s it about?
Phil Motta is the senior author, with 11 co-authors from Georgia Aquarium, Mote marine lab, Project DOMINO and the University of California. Eleven seems like a lot of co-authors, but it’s a very comprehensive and very broad ranging look at feeding in the worlds largest fish.
First the what. Many folks are aware that whale sharks are filter feeders, meaning that they swim the worlds oceans sieving tiny food particles from the water. That much was fairly obvious from their enormous mouths and 20 filter pads that are visible inside. What wasn’t known was exactly what they eat and how much, especially relative to how much energy they spend, a balancing act we can call the energy budget. For the first time, Phil and his colleagues were able to measure the size of the whale sharks mouth, how much time they spend with it open and the speed at which they swim, and from that the amount of water that they filter in an average day. By combining that with measurements of plankton density in the coastal waters of Mexico where whale sharks gather and nutritional analyses of samples taken there, they worked out how much whale sharks eat in that natural setting. The answer: between 1.5 and 2.7 kg (3-6lbs) an hour, scaling up to between 15 and 30,000 kilocalories a day (up to 125,000 kilojoules). Not surprisingly, the amount of plankton in the water was higher where whale sharks were eating than where they were not, mostly due to calanoid copepods and sergestid shrimps (one of which, with the cool genus name of Lucifer, is illustrated below). That could mean whale sharks really like those items, or just that they really like dense patches of food, and those ones just happened to be shrimps and copepods. Or it could be both.
Some of the coolest stuff in the paper, though, is about HOW whale sharks feed. They filter, yes, but not like baleen whales and not like other filter-feeding fishes. A baleen whale takes a huge mouthful of water and then squeezes it out through their baleen combs, which trap the food items, like pasta gets caught in a colander. Thats a perpendicular or dead-head filter, and the problem with those is that they have to be backflushed from time to time to blow the particles off the screen (left panel below). In whale sharks, on the other hand (right panel below), water flows mostly parallel to the filter surface, only deviating slightly to dip across the filter surface and siphon out through the gills. Food particles, which have more momentum, don’t get trapped on the filter but carry on to the back of the mouth, forming an ever more concentrated ball of food. This is the same principle behind plankton nets and its very efficient because the filter doesn’t clog up with particles the way a baleen plate (or standard kitchen colander) would, and it rarely needs backflushing.
Its an ingenious system, illustrated nicely in the figure above from Elizabeth Brainerd’s 2001 paper in Nature.
I could go on all day about whale sharks and their feeding, or you can skip the middle man and go get the PDF of Phil’s paper here. Its well worth a read; there are some great images and a far more interesting and detailed discussion than the precis I have here. Check it out. You can learn more about Georgia Aquarium whale shark research from the tag list on the left, or by going here.
Motta, P., Maslanka, M., Hueter, R., Davis, R., de la Parra, R., Mulvany, S., Habegger, M., Strother, J., Mara, K., & Gardiner, J. (2010). Feeding anatomy, filter-feeding rate, and diet of whale sharks Rhincodon typus during surface ram filter feeding off the Yucatan Peninsula, Mexico Zoology DOI: 10.1016/j.zool.2009.12.001
Brainerd, E. (2001). Caught in the Crossflow Nature, 412 (6845), 387-388 DOI: 10.1038/35086666
Some of the work we did in Mexico this summer will be featured on the National Geographic blog Inside Wild over the last quarter of this year. The latest installment penned by Jodi Kendall, who accompanied us to Mexico, can be found here. Check it out, and watch that space for future installments! Learn more about Georgia Aquarium whale shark research here.